1. Field of the Invention
This invention relates to method and apparatus for conveying individual blanks of sheet material and, more particularly, to method and apparatus for engaging the leading blank in a group of overlapping blanks and separating the leading blank from the group of overlapping blanks.
2. Description of the Prior Art
It is conventional practice in many sheet feeding operations to advance sheets of material in overlapping relation along various stations of a processing machine such as a drying station in an envelope making machine. At some point, it is often desired to remove the sheets from overlapping or shingled relation into spaced tandem relation thereby enabling subsequent operations to be performed on individual sheets.
To separate a first sheet from a group of overlapping sheets, a pull-out segment roller is conventionally utilized to frictionally engage the leading edge of the first sheet and accelerate it out of overlapping relation with the remaining sheets. Several examples of conventional friction separation mechanisms are illustrated in U.S. Pat. Nos. 1,153,533 and 3,379,432.
U.S. Pat. No. 1,153,533 discloses apparatus for aligning envelope blanks. A series of overlapping blanks are positioned at the entry portion of the machine. The bottom edge of the first blank partially rests on a backing roller. A rotating segment roller is positioned in parallel relation to the backing roller and a pull-out segment is rigidly mounted on the segment roller. The segment roller is positioned so that as it rotates the outer surface of the pull-out segment frictionally engages the leading edge of the first blank resting on the backing roller. The rotating pull-out segment grips the leading edge of the first blank and removes it from overlapping relation with the remaining blanks.
In U.S. Pat. No. 3,379,432, a group of overlapping envelope blanks are positioned before a rotary aligner mechanism. Prior to alignment, the blanks are separated from overlapping arrangement by a pull-out segment device similar to that disclosed in U.S. Pat. No. 3,153,533. A cylinder having a withdrawing roller segment frictionally engages the leading edge of the topmost blank in the group. The action of the withdrawing roller segment against its associated counter-roller grips the topmost blank and removes it from overlapping relation.
The frictional separation of blanks by a pull-out segment, though well known and used, is not without its drawbacks. It has been found that depending upon the weight and style of paper to be fed, frictional separation can cause marks to appear on the blank. The marks are often visible in the finished product and detract from its overall quality. To counteract the formation of marks, it is well known to utilize vacuum cylinders to separate overlapping blanks. Several examples of conventional vacuum style separators are illustrated in U.S. Pat. Nos. 1,045,551, 2,406,765, and 4,345,752; Japanese Patent No. 56-61243; and Xerox Disclosure Journal Vol. 9, No. 6, November 1984.
In U.S. Pat. No. 1,045,551, a segmented rotating vacuum separator cylinder is used to separate the topmost sheet from a stack. A series of ports receiving negative pressure are located on the outer surface of the vacuum separator cylinder and at a point in the cylinder's rotation, the ports are positioned in close relation to the topmost sheet in the stack. The negative pressure at the ports causes the topmost sheet (and possibly several adjacent sheets) to adhere to the surface of the vacuum separator cylinder. The rotation of the cylinder lifts the sheet(s) away from the stack and on to subsequent operations.
Means is also provided to prevent the separation of more than one sheet at a time. As the sheet(s) are rotated on the surface of the vacuum separator cylinder, an adjacent frictionally coated cylinder rotates into close parallel relation to the sheets. The frictional surface of the adjacent cylinder lightly grazes the separated sheets and causes all but the first sheet to release from the vacuum separator cylinder and return to the stack, thereby preventing more than one sheet to be separated from the stack simultaneously.
U.S. Pat. No. 2,406,765 also discloses a vacuum separator mechanism in which the topmost sheet in a stack is positioned for removal from the stack by a rotating cylinder having a vacuum port on its outer surface. As the cylinder rotates, the vacuum port becomes positioned adjacent the upper surface of the topmost sheet. A blast of air lifts the topmost sheet and causes the sheet to adhere to the vacuum port in the rotating cylinder. Subsequent blasts of air cause the remaining length of the topmost sheet to be separated from the stack. Movement of the vacuum cylinder forces the topmost sheet to enter a set of feed rollers which advance the topmost sheet to subsequent stations in the machine away from the stack.
U.S. Pat. No. 4,345,752 and Japanese Patent No. 56-61243 disclose a device for separating the topmost blank from a stack of blanks. A cylinder having a plurality of vacuum ports in its outer surface is rotated very close to the upper surface of the topmost blank where its rotation is momentarily halted. Vacuum pressure exerted through the ports lifts the topmost blank into engagement with the vacuum cylinder and the further rotation of the cylinder removes the sheet to subsequent operations. Additional vacuum ports adjacent to the stack engage the blanks immediately below the topmost sheet to prevent these blanks from becoming separated along with the topmost blank.
Xerox Disclosure Journal Vol. 9, No. 6 dated November 1984 discloses a device for removing and placing labels in a labeling machine. A plurality of vacuum pads are spaced apart on a cylinder. As the cylinder rotates, each pad engages a label to its surface by vacuum pressure. Subsequent rotation of the cylinder puts the pad in a position adjacent the surface of a document. The vacuum pressure is removed and the label is affixed to the document at that location.
When separating blanks from a moving overlapped group, the speed of the first blank must be substantially increased from the remainder of the group to facilitate the complete separation of the blank. Such speed increases are typically on the order of 10:1. That is, the speed of the first blank is removed at ten times the speed of the entire group.
It has been found that blanks separated from overlapping relation by vacuum separating devices, while effectively separated from the group, are displaced from a preselected registered position in the feed path. The rapid acceleration of the separated blank cannot be immediately accomplished by vacuum pressure and, therefore, some degree of slippage occurs causing the blank to lag slightly behind its desired position. For this reason, many separating mechanisms still utilize the frictional separating devices described above.
Therefore, there is a need in sheet feeding operations for a sheet separating device which enables an operator to choose a method of separation, either frictional or vacuum, depending upon the circumstances presented to him.
There also remains a need for an envelope blank separating device which can be efficiently adjusted to separate various sizes and styles of envelope blanks from overlapping relation into spaced tandem relation.